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Proof That the Universe is Electrically Neutral

  1. Feb 13, 2008 #1
    What evidence do we have to support the assertion that the universe is electrically neutral on large scales?

    I know that gravity is the dominant force on large scales but what kind of evidence can we give to support the above statement? Does it suffice to say that we have the same number of protons and electrons?
    Last edited: Feb 13, 2008
  2. jcsd
  3. Feb 13, 2008 #2
    Just out of interest.. Is there a theory that states that the universe is electrically neutral?
  4. Feb 13, 2008 #3
    Well not a theory maybe but we know that the universe is electrically neutral. You don't suspect we live in an ionized universe, do you?
  5. Feb 13, 2008 #4
    It's all a question of quantities. I don't suspect the universe is significantly ionized, however I don't see any proof to suggest that the universe is completely balanced either. If there was a very insignificant number of charged particles of one type which would be more common in the universe would we really know? As a matter of fact I have previously though about what exactly would happen if there was a slight charge to the universe. If you take on this though experiment some interesting conditions arise.
  6. Feb 13, 2008 #5
    Well maybe I didn't mean "proof" but instead I meant "evidence"

    It seems to be an agreed upon fact that the universe is electrically neutral, on large scales.

    What's the evidence? One way to think about it so to try and answer the question that you asked: What would happen if the universe wasn't neutral? How would the universe be like then?
  7. Feb 13, 2008 #6
    I guess you might not have heard of the IGM (intergalactic medium) which could be considered to constitute the majority of the universe. The IGM is ionised.

    I don't think there is any good observational evidence that the universe is charge-neutral.

    I'd be interested to hear from anybody in the know who can say whether charge-neutrality of the universe is a feature of the hot big bang theory.
  8. Feb 14, 2008 #7
    Well, I think we assume the universe started out with no charge, so tehrefore when particle decays took place (pair production) and split into a positron/electron, and such things.

    Conservation of charge?
  9. Feb 14, 2008 #8


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    There seems to be a lot of confusion in this thread. To clarify, the Universe is indeed mainly ionized, and has been for many Billions of years ( look up 'epoch of re-ionization' for more info). This, however, has nothing to do with whether the Universe is electrically neutral. If something is ionized that simply means the positive and negative particles (atomic nuclei and electrons) are separated. It doesn't mean that the overall charge is not neutral. The total charge of something (including the Universe) is a completely separate issue to the ionised fraction.
  10. Feb 14, 2008 #9
    So is the universe charged or not?
  11. Feb 14, 2008 #10
    I don't think anyone knows on very large scales (greater than 10^9 light years).

    This article suggests that locally, in the vicinity of the Milky Way galaxy, on a scale of 10^5 light years, space is dominated by ionized gas. I haven't seen anything yet that suggests that postively ionized gas has been found over here and negatively ionized gas has been found over there. Since the universe is mainly ionized, I would have to conclude that locally, on a scale of 10^5 to 10^7 light years, it is also electrically charged, unless observations of opposite ionization have been made....fill me in if those observation have already been made.....

    If the universe is electrically non-neutral out to a scale of over a billion light years, what are the implications? Where are the missing electrons (or atomic nuclei)?? Were they ever there??? This seems like a very fundamental question that should be discussed and resolved or very basic models are seriously flawed.
    Last edited: Feb 14, 2008
  12. Feb 15, 2008 #11


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    Wallace has clarified the issue here. There is the question of overall neutrality.

    Cadnr and presumably almost everybody here knows that the universe is largely ionized. So that has no relevance to the issue of overall neutrality.
    Sysreset offered evidence that there is some ionized gas somewhere, but that is irrelevant. It does not indicate that the ionized gas fails to be overall neutral.

    We all know the interior of the sun is largely ionized----most of the hydrogen nuclei and the electrons are running around separately instead of being paired up in atoms. BUT THE SUN GIVES EVERY SIGN OF BEING overall NEUTRAL.

    In science when you make a statement it is supposed to be true within some errorbar or within some tolerance. So Cadnr, would you be happy with an assurance that the universe is neutral WITHIN ONE PART PER BILLION? What would satisfy you?

    Can anyone tell us what would happen if the sun had one ppb too many electrons?

    Can anyone estimate what would happen if our Milky Way galaxy had one ppb too many protons?


    For that matter, how about if the Milky Way deviated from electrical neutrality by one part per trillion?

    this is a simple back of envelope calculation. It would be exploding. we can go higher, but I don't know how close to perfect neutrality Cadnr wants.
    Last edited: Feb 15, 2008
  13. Feb 15, 2008 #12
    Hi Marcus,

    Are you saying you have proof that the Milky Way galaxy is electrically neutral, to, say, one part per quadrillion? Since it is largely ionized, there must be structures that are negative and some that are positive to balance it out. On what scale are these separately charged structures, and has anyone attempted to create an image of this, for our galaxy or any other galaxy?
  14. Feb 15, 2008 #13


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    I'm not sure what you have in mind by "structures". You speak of mapping. I assume you mean some macroscopic structures that would be visible on a galaxy map. Maybe you could be more definite about what structures you mean and why you think they must have a net electric charge.
  15. Feb 15, 2008 #14


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    Your conclusion does not follow from your premise. If a gas in ionized it simply means that some electrons have seperated from the constituant atoms (or molecules) that make up the gas leaving positively charged atoms/molecules and negatively charged electron. However they are still mixed together in the same gas, the 'seperation' that you assume does not exist. The positive and negative charges still mingle in the same space. Even if you took a very small volume (the size of a grain of sand) of an ionized gas the overall charge is still neutral.
  16. Feb 15, 2008 #15
    I get it now, thanks. You've answered my question marcus and wallace.
  17. Feb 15, 2008 #16
    It would blow up with a bang that would make a supernova look like a firecracker?

    The mass of the sun is 1.99×10^33 g, so it has 1.99^10^33 * (6.022 * 10^23=avogrado's number) = 1.24 * 10^57 Electrons. This is a charge of about 2*10^38 coulomb (assuming everything is hydrogen) using a 1 ppb surplus we still have 2*10^29 coulomb of charge. The repulsive force due to this is (charge of the sun)*(coulombs constant)/[(mass of sun)*Gravitational constant] wich is about 10^16 as big as the gravitational attraction.

    I think it's safe to say that the charge imbalance of the sun must be < 10^-25.

    It seems likely to me that the sun probably has a small positive charge, because it's easier for electrons in the solar wind to get away than for heavier positively charged ions.
  18. Feb 19, 2008 #17


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    We have good evidence there is a slight imbalance in the total charge of the universe. If the universe was charge neutral, matter would be nearly extinct by now. Quantum uncertainty does not permit a static universe.
  19. Feb 22, 2008 #18
    Just out of curiosity what sources are there for this, and just what do you mean by a slight imbalance? i.e how slight? 1 part per quintillion?
  20. Feb 22, 2008 #19


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    Can you elaborate Chronos? This doesn't sound right to me. Can you indicate where you got this from?

    I'm not sure how we suddenly got to a static universe in a discussion about whether it has a neutral overall charge??
  21. Feb 22, 2008 #20


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    Amongst others, there is the evidence of CMB isotropy. A charged universe would feature currents which would show up in the spectrum.
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